Nozzle and torch for plasma jet

ABSTRACT

A plasma jet nozzle is characterized by a plasma jet flame opening mainly in the form of a slit which produces a stable and powerful jet flame in the form of sheet-film or sector, and a long and slender cylindrical plasma jet torch with a slit nozzle fixed at the end is characterized by its use for boring deep into reinforced concrete.

United States Patent I Shinroku et al.

Sept. 4, 1973 NOZZLE AND TORCH FOR PLASMA JET inventors: ,Sailo Shinroku, Suginami-ku, Tokyo;

Yukihiko Okada, Higashicho, Musashino-shi, Tokyo; Naoki Negishi, Setagaya-ku, Tokyo, all of Japan Assignee: Kogyo Kaihatsu Kenyusho, Tokyo,

Japan Filed: Feb. 2, 1971 Appl. No.: 111,867

Related US. Application Data Continuation-impart of Ser. No. 771,496, Oct. 29, 1968, abandoned.

US. Cl 239/1323, 219/75, 239/599 Int. Cl. H0lj 17/26 Field of Search 239/128, 132, 132.1, 239/1323, 597, 599, 601; 219/74, 75, 121, 122; 137/801 [56] References Cited UNITED STATES PATENTS 2,666,122 l/l954 Curtin et a1 219/123 2,928,933 3/1960 Andriola 219/74 X 3,450,926 6/1969 Kieman 219/75 X 3,179,782 4/1965 Matvay 219/75 X Primary Examiner-M. Henson Wood, .lr. Assistant ExaminerMichae1 Mar Attorney-Christen & Sabol [57] ABSTRACT A plasma jet nozzle is characterized by a plasma jet flame opening mainly in the form of a slit which produces a stable and powerful jet flame in the form of sheet-film or sector, and a long and slender cylindrical plasma jet torch with a slit nozzle fixed at the end is characterized by its use for boring deep into reinforced concrete.

14 Claims, 44 Drawing Figures PATENTEDSEP 4m 375651 1 sum 1 or 6 FIG.2'(o) PATENTEDSEP 4 ms 3.75s; 5 1 1 SHEET 2 0F 6 II\ 4 I Z @mea 5 F I 8(a) Pmminsznma 3756511 SHEET 5 [IF 6 PATENTEDISEP 4191a 3.7561511 SHEET 6 BF 6 FIG.24(0) NOZZLE AND TORCH FOR PLASMA JET This application is a continuation in part of our copending application, Ser. No. 771,496, filed Oct. 29, I968 now abandoned.

The present invention relates to a nozzle and a torch for the plasma jet.

In recent years the plasma jet has begun to find a wide application because of its capability to give a very high temperature. For example, it is used not only for cutting metals and refractory materials but also for producing a static super-high temperature by an arc image furnace, and its unique performance is evaluated to be quite excellent.

On the other hand, however, this plasma jet has some difficult problems still to be solved such as instability of flame, no variety of the form of flame and complicated structure of torch required for giving spiral motion of gas within the plasma torch. To solve these difficulties, various attempts have been made, but no striding growth has been made.

The object of the present invention is to provide a new plasma jet flame characterized by stability, powerfulness, low cost, unique shape and a very wide field of application.

The inventors of the present invention have been conducting researches over many years to apply the plasma jet to the cutting and boring of reinforced concrete and as a result have made an invention of a nozzle and a torch capable of producing quite a new plasma jet flame.

In the attached drawings,

FIG. 1a is a fragmentary cross-section of a conventional nozzle;

FIG. lb is an end view looking upwardly at the nozzle of FIG. 10;

FIG. 2a is a fragmentary cross-section of a preferred form of nozzle having a slit opening in accordance'with the present invention;

FIG. 2b is an end view of the nozzle of FIG. 2b;

FIG. 3 illustrates the plasma jet flame issuing in the form of a film;

FIG. 4a shows a cross-section taken at right angles to FIG. 2a;

FIG. 4b is the end view of the nozzle of FIG. 4a;

FIG. 5a illustrates the formation of a conical surface at the end of the nozzle adjacent the electrode; in FIG. 5b the space is generally ellipsoidal, while in FIG. 50 the conical surface is shown extending through the length of the nozzle;

FIG. 6a illustrates the formation of a slit surface by a tool which enters from the face of the nozzle, as shown in FIG. 6b;

FIG. 7a illustrates the resulting combination of interior surfaces resulting from the operations of FIGS. 5 and 6;

FIG. 7b is a view of the face of the nozzle of FIG. 70;

FIGS. 8a and 8b are corresponding views, but taken at right angles to FIGS. 7a and 7b;

FIG. 9 is a perspective view of a nozzle indicating the various dimensions which influence the jet flame;

FIG. 10a is a cross-section of a modified form of nozzle in which the slit tapers outwardly toward the outlet;

FIG. 10b is a view of the end surface of the nozzle of FIG. 10a;

FIG. 11 illustrates the sector-shaped flame produced by the nozzle of FIGS. 10a and 10b;

FIG. 12a illustrates a form of nozzle having radial cooling fins;

FIG. 12b is an end view of the nozzle of FIG. 12a;

FIG. 13a is a longitudinal cross-section of a rod-type plasma torch provided with a nozzle according to the present invention;

FIG. 13b is a view of the lower end face of the torch of FIG. 13a;

FIGS. 140, b and c respectively illustrate diagrammatically various configurations of narrow slit openings in a nozzle;

FIG. 15a shows a nozzle with longitudinal cooling fins taken on the cross-section EE of FIG. 15b which is an end view of this nozzle;

FIG. 16 is a cross-section taken on the line AA' of FIG. 13a;

FIGS. 17 23 illustrate diagrammatically various other configurations for a nozzle outlet opening;

FIG. 24a is a cross-section of a nozzle having an angularly directed slit opening;

FIG. 24b is an end view of the nozzle of FIG. 24a;

FIG. 24c illustrates the shape of the flame produced by the nozzle of FIGS. 24a and b;

FIG. 25a is a cross-section of another form of angled slit;

FIG. 25b is an end view of the nozzle of FIG. 25a;

FIG. 25c illustrates the shape of the flame produced by the nozzle of FIGS. 25a and b, and;

FIG. 26 is a cross-section of a typical nozzle indicating the rounded edge which may be used along the intersection of the slit with the end face.

As shown in FIG. 1, the conventional nozzle has a circular opening 3 for jetting the plasma flame in the plasma flame jet face 2 at the bottom of the nozzle 1. The upper part of the nozzle has also an opening for example in the form of a cone according to the shape of the tungsten electrode rod 4, and the gas passes through the nozzle with'a spiral motion and its thermal pinch effect is given at the jet opening 3.

We found out that this thermal pinch effect is dependent on the ratio of the sectional area of the jet opening 3 to the length of the surrounding wall of the jet opening 3, and after many trial manufactures and tests of nozzles, we have found that with the same sectional area, the thermal pinch effect increases with larger ratio of the length of surrounding wall B to the sectional area A: B/A. This shows that with the same sectional area, a rectangularshape or further a slit-like shape of the jet opening 3 is more desirable than a circular opening. This finding has led the inventors to the invention of quite a new nozzle shape, namely, a slit- Iike nozzle, and surprisingly enough, it has been found out that the use of such a slit-nozzle makes it unnecessary to provide the spiral motion of gas which has been thus far regarded as indispensible for the plasma jet torch and a mere turbulent flow of gas itself determined by the Reynolds number at the nozzle is sufficient. These will be explained in more detail in the following with reference to the drawings.

FIGS. 2a and 2b show a slit-nozzle of the present invention. As is obvious from these Figures, the plasma flame jet opening 5 in the plasma flame jet face 2 at the bottom of the nozzle 1 is designed with a slit form. The plasma jet flame emitted through such a nozzle has a shape of a thin film as shown in FIG. 3. This is a shape of a plasma jet flame that has never been available.

FIG. 4a shows a side view of the nozzle of FIG. 2a. Irrespective of the shape of the upper opening 7, it is possible to produce a flame of such a form by designing the jet port 5 as a slit opening.

As regards the space in the nozzle between the slit at the plasma jet face and the part near the tungsten electrode rod, i.e., the opening 7 of the electrode surface 6 of the nozzle 1, it is designed as a combination of a variously shaped space 8 such as a cone, a pyramid, a hemisphere and an ellipsoid of revolution made at the opening part 7 of the electrode surface 6 as shown in FIGS. 5 a, b and c and a slit structure space 9 formed from the plasma flame jet face 2 as shown in FIG. 6. For example, if 8 is a conically formed space, such a conical space 8 made downward from the upper opening part 7 is combined as an overlapping form with the slit-like space 9 formed upward from the plasma flame jet face 2 as shown in FIG. 7 and in FIG. 8 which is a side view of the structure shown in FIG. 7.

The form of the space 8 varies chiefly according to the form of the electrode rod and an adequate form must be selected. In addition, the form of the space 8 is supposed to be dependent on such factors as the flow rate of gas used for plasma jet, voltage, electric current, gas composition (argon, hydrogen, nitrogen, air, combustion gas or misture thereof), required for the power of the jet plasma flame in the form of a flame, etc.

Now explanation will be made about the variety of the form of the slit nozzle. First a model of slit is assumed as shown in FIG. 9. This is a slit as shown in Figures up to FIG. 8. To indicate the dimensions of the plasma flame jet opening 5, symbols W, H and L are used, denoting the width 10, height 11 and length 12 of the slit respectively.

FIG. shows a variety of this slit form, in which the electrode surface 6, its opening part 7 and the conical space form 8 are the same as before, but the slit-like space 13 from the plasma flame jet face 2 is different from the above-mentioned regular slit form. As can be seen from the Figure, the slit beginning from the jet face 2 extends upwards to a suitable height II of the nozzle 1, namely up to 14 in this Figure. The length l of the slit becomes gradually shorter as it rises, thus a slit space is made in the form of a sector. In other words, the length of the slit becomes larger as the jet gas proceeds. In this case, the width of the slit remains unchanged. The spaces of 8 and 13 are formed in this way, the two spaces overlapping each other to form a passage characterized by a modified slit form.

With the standard form of a slit-nozzle as shown in Figures up to FIG. 8, the plasma jet flame has a form of a film (14 in FIG. 3), but with the modified slitnozzle of FIG. 10, the plasma jet flame is characterized by a form of a thin sector (15 of FIG. 11). The plasma jet flame formed by the slit nozzle according to the present invention has many new applications. For example, in case of cutting a metal plate or refractory material, a very thin cutting is possible if the nozzle is moved in the direction of the slit length, while a cutting with a large width is possible if the nozzle is moved in the direction of the slit width. If the nozzle is rotated around its axis, a circular boring will be effected, and if the nozzle is moved forward while rotating, cutting and boring will be effected in a variety of forms. The greatest advantages of this slit nozzle, however, are large thermal pinch effect and high and uniform density of the flame, which produces a stable flame and large heat output. The jet flame emitted from this slit nozzle is so powerful that it can give a cutting speed 1.5 times as high as that of the previous plasma jet flame, or with the same cutting speed, the power consumption by the new slit nozzle is far smaller than that in the case of the conventional nozzle and the cut surface is much neater. With the modified form of the slit nozzle, the flame is produced in the form of a sector having a much larger length than the diameter of the nozzle itself. When such a variety of the slit nozzle is used for cutting work, another effect will be added to those mentioned above, namely, such a sector flame will make it possible to cut with a larger width than the standard slit nozzle, and if rotation of the nozzle is combined with such sector flame, a boring will be made with a larger diameter than that of the nozzle itself, the hole being so large that the complete torch is allowed to be inserted into the hole. Therefore, such a sector slit nozzle will find applications, for example in making deep holes by bormg.

The effects of the slit nozzle for the plasma jet ac cording to the present invention may be summarized as follows:

1. Thermal pinch effect is large and the flame density is high and uniform.

2. Since the flame can be produced with a very small width, the slit nozzle is most suitable also for making a plasma jet flame for the arc image furnace.

3. Plasma jet flame is very stable.

4. Thermal output is large and the jet flame is powerful and economical.

5. When it is applied to cutting and boring, the speed -of cutting or boring is very high.

6. It is possible to cut with a small cutting width.

7. It is possible to cut with a large cutting width.

8. By changing the direction of the slit-formed flame from the advancing direction of the torch, it is made possible to cut with a freely adjustable width. This width is adjustable at any desired time.

9. The cut surface is very neat.

I0. Rotation of the modified slit nozzle produces easily a hole having a diameter larger than that of the nozzle itself, so that such a nozzle is suitable also for boring of a deep hole.

Thus it is obvious that the slit nozzle has truly great effects. As mentioned above, the nozzle of the present invention increases the thermal pinch effect substantially, but still there are methods to further increase the thermal pinch effect as illustrated in FIG. 12 or FIG. 15. The 17 of FIG. 10 indicates an external water cooling wall surface. If this wall surface is provided with one or more fins 16 or ribs which will serve for heat conduction as shown in FIG. 12 or FIG. 15, the heat conductive surface area will be greatly increased. This will result in greater cooling effect, which will increase the thermal pinch effect. As a result, a more powerful plasma jet flame in the form of a film or a sector will be produced.

In the meantime, it was also found out by further researches that with the above-mentioned slit nozzle, the spiral motion of the gas which has thus far been considered to be indispensable for the plasma jet torch becomes almost unnecessary and that the turbulent flow of gas itself specified merely by the Reynolds number at the nozzle is sufficient.

This may be attributable to the fact that in the previous plasma jet torch a nozzle form having a relatively small thermal pinch effect was used and this insufficient pinch effect had to be made up by a powerful spiral motion of gas. Therefore, with the use of the slit nozzle of the present invention, it is possible to produce a sufficiently powerful plasma jet flame in the form of a film or a sector without using a specially generated spiral motion of the gas. This elimination of the spiral motion makes it possible to design the gas piping of the torch as a straight pipe, making the torch itself slender, more simplified and less costly.

FIG. 13(a) and FIG. 16 show a rod-type plasma jet torch of the present invention, in which a slit nozzle of a modified form 1 is used. FIG. 13b shows a nozzle viewed from the plasma flame jet face. In the Figure, 4 is a water-cooled tungsten electrode rod disposed at the central axis of the torch. Around this electrode rod there is a concentric hollow cylinder 18 to provide the passage of gas, which is further surrounded by another concentric hollow cylinder 28 to provide the passage for cooling water 27. The direction of the flow of the cooling water is indicated by 19. 21 and 22 are electric wires connected respectively to the electrode rod 4 and the nozzle 1. The cooling water cools also these wires. The plasma jet gas enters the torch through 23 as indicated by an arrow and flows in the torch in the direction of the arrow 20 without making any specially designed spiral motion. The gas flows thus to the nozzle having an outlet of the plasma jet flame 5 in the form of a slit as already explained above. The torch itself has a slender rod-like form. In this FIG. 13, the form of the slit nozzle is that shown in FIG. 10, but it is of course possible to use the standard slit nozzle form as shown in the Figures up to FIG. 8 and the modified form shown in FIG. 12 and thereafter.

The torch according to this invention has a simple structure and accordingly can be manufactured at low cost. Therefore, a stable, powerful and unique plasma jet flame can be produced at low cost and in a very thin form. This makes the torch suitable also as a plasma jet torch for boring work. The slender rod-like for of torch mentioned above does not mean only a straight rod form. It may be a suitably curved form according to the desired boring shape. Thus the rod-like in this invention includes a curved rod.

The slit-like structure of the slit-like nozzle of the present invention means a generally narrow opening. This may be in a variety of form, i.e., it may be a long rectangular form as shown by FIG. 14a or a similar shape with rounded corners as shown by b or a convex as shown by c of FIG. 14. In any case the form must have a considerably larger length (L in FIG. 9) than the width (W in FIG. 9) in the plasma jet face 2.

The nozzle of this invention can be designed so as to have a deflected slit. In this case, the plasma flame will be produced in a direction somewhat inclined against the axial direction of the torch (FIG. 24c and FIG. 25). If a torch having such a deflected slit is rotated around its axis, the boring will have a further greater diameter. This deflection can be made chiefly at the slit, for example, at 24 of FIG. 4 or at 24 of FIG. 2 in the direction of the slit width or length respectively (24 of FIG. 25 and FIG. 24). The nozzle may also be deflected at 14 of FIG. 10.

In case of using this nozzle for boring, it may be provided with an orifice or a port for jetting water or gas (e.g., air) through the plasma flame jet face. This will serve for discharging the melt out of the bored hole. An

example of such a jet orifice for jetting water or gas is shown by 25 in FIG. 8a and b. The nozzle may be provided with one or more of such orifice. If water or air is jetted in case of boring reinforced concrete, melted concrete will be cooled rapidly and become fine powder, which is very easy to discharge from the bored hole.

The following nozzle forms are also included in the scope of the present invention: Two or more slits conforming to the present invention are made in the plasma flame jet face as shown in FIG. 17 and FIG. 18; the slit is bent or curved at one or more positions as illustrated, in FIG. 19 and FIG. 20; various cross slits are illustrated in FIG. 21, FIG. 22 and FIG. 23.

Further,the jet slit of all the nozzle according to this invention may have a rounded edge instead of a sharp edge at the plasma flame jet face as shown by 26 of FIG. 26. Such a rounded edge has an effect of making the jet flame a little longer than usual.

Thus, according to this invention, it is possible to obtain easily a new plasma jet flame which is stable, powerful and of low cost and has a unique shape and a very wide scope of application.

The following examples will further illustrate the nature of this invention but the invention is not restricted to these examples.

EXAMPLE 1 Nozzle of this invention Conventional nozzle Shape of plasma flame jet opening Gas composition Voltage Electric current Shape of plasma Speed of cutting iron sheet (20 mm thick) Width of cut in the same case as above Width of slit l.2mm Length of slit 10mm Height ofslit 9mm Ar 95% Thickness of flame ca. 2 mm Width of flame ca. 10mm Length of flame ca. 30mm Flame in the fonn of thin film 200-300 mm per minute to mm in case of moving the nonle in width direction of slit 4 mm in case of moving the nozzle in length direction of slit circle of4mm dia.

Diameter of flame ca. 5mm

Length of flame Flame in the form of a slender cone mm per minute EXAMPLE 2 When the modified slit nozzle of this invention as shown in FIG. 10 was used instead of the standard slit nozzle used in Example I, the result was as follows:

Nozzle of this invention Shape of plasma flame jet opening 10 mm Slit in the form of a sector Gas composition Ar 95% H, Voltage 95 V Electric current 300 A Flame in the form of a thin sector Thickness of flame ca. 2 mm Width of flame near the plasma flame jet face: ca. 13 mm Width of flame at a flame length about 30 mm: 25 mm Shape of plasma jet flame Speed of cutting iron sheet (20 mm thick) Width of cut in the 200-350 mm/min 15 mm in case of moving the nozzle in width direction of slit 4 mm in case of moving the nozzle in length direction of slit same C386 85 above EXAMPLE3 The experiment was conducted by using a torch in the form of a straight rod (as shoen in FIG. 13) with the following specification:

The torch is provided with a thin steel electrode rod (5 mm 4;) having a tungsten electrode at its top; at its outside, a first concentric cylinder for passage of gas with an inside diameter of mm; a second concentric hollow cylinder for passage of cooling water with an inside diameter of mm; diameter of torch 17mm; length of torch about 1 m. At the top of the torch was connected a slit nozzle having a modified slit form of this invention as shown in FIG. 10 (the nozzle being provided with a water jet orifice as shown in FIG. 8). Argon gas was fed at a rate of 5 kg/cm, lit./min. and a voltage of 30 V as applied. Under these conditions, electric current was passed and the torch was put into operation, by which almost the same plasma jet flame as in Example 2 was produced and maintained. Under the influence of water jet, this plasma flame was a little inclined to the opposite side of water. During about one hour, the flow rate and voltage were changed in a wide range, and the torch was swayed to various directions and further subjected to vibration, but the flame was kept in stable condition all the time.

This torch was also used for boring reinforced concrete having a thickness of about 300 mm. During this use, the torch was turned around its axis, and by the effect of water jet, the melt gushed in the form of fine powder together with the water from the upper opening of the hole. In two and a half minutes, a hole was completely bored into a depth of 300 mm. Nearly the same results were obtained by using air jet instead of water jet. Needless to say, the torch itself was brought into the hole as it was bored deeper.

EXAMPLE 4 Various cutting experiments were conducted under the same conditions as in Example 1 to measure cutting speeds and the following results were obtained:

450 mm/min. with aluminum sheet having a thickness of 12 mm, and ,250 mm/min. with 30 mm thick concrete slab. In case of cutting in water, 220 mm/min. with 12 mm thick aluminum sheet, 90 mm/min. with 9 mm thick iron sheet and 80 mm/min. with 40 mm thick concrete slab. Since the conditions of experiments were not optimum, it has been ascertained that the cutting speed will be further increased through future reasearches. It has also been ascertained that it is possible to generate and maintain safely air plasma and nitrogen plasma as well.

EXAMPLE 5 As mentioned above, it is desirable that the ratio of the length of the surrounding wall B to the sectional area A, i.e., B/A, of a slit-like nozzle should be large. The results of an experiment conducted with varying ratios are as follows. For the experiment mixed gas of Ar (95percent) and H (5 percent), 280-320 amps of the electric current and -95 volts of the voltage were used. The evaluation of the results was divided into the following four grades depending on the amount of gas, voltage and vibration. The highly stable grade is indicated by the symbolz the stable grade by O; the slightly stable grade by A; and the utterly unstable grade by X.

Type of nonle A(mm) B B/A Evalu (mm) ation width(mm) length(mm) 1.2 10.0 (slit) 12.0 22.4 1.87 '9 0.6 12.0(s1it) 7.2 25.2 3.50 2.0 8.0 (slit) 16.0 20.0 1.25 0 1.6 10.0 (Slit) 16.0 23.2 1.45 1.2 15.0 (slit) 18.0 32.4 1.80 2.5 8.0 (slit) 20.0 21.0 1.05 A 2.0 10.0 (slit) 20.0 24.0 1.20 O 1.0 10.0 (slit) 10.0 22.0 2.20 2.3 10.0 (slit) 23.0 24.6 1.07 A 3.0 10.0 (slit) 30.0 26.0 0.87 X 1.65 12.0 (sectorial) 19.8 27.3 1.38 1.35 12.0 (sectorial) 16.2 26.7 1.65 G) 1.2 22.0 (cross) 49.4 84.8 1.72 4 (circular) 12.5 12.5 1.00 O

5 (circular 19.6 15.7 0.80 A

6 (circular) 28.3 18.8 0.67 X

According to the above-mentioned equipment, each of the slit-like nozzles, sectorial nozzles, and cross nozzles of our invention showed a remarkable result when B/A was over 1.00 and preferably over 1.20, and particularly when B/A was over 1.4 the result was highly stable. The width of the slits was found to be limiting, and widths over 2.5 mm were found to be undesirable while widths under 2.0 mm were found to be preferable. On the other hand, in the case of a conventional circular opening, the result of an experiment showed that 4 mm (BIA 1.00) was stable and over 5 mm was unstable. Consequently, a slit-like shape of a jet opening of our invention is to be evaluated on a different basis from that of the BIA of a conventional opening.

Thus it is desirable to make the ratio B/A larger, and as is clear in Example 5 a good result is obtained when B/A is over 1.00, preferably over 1.20 and particularly over 1.4. As far as the results of the experiment are concerned further limitation may be provided by the selection of the width of the slit under 2.5 mm, preferably under 2.0 mm. This basis is quite different from that of a circular nozzle under 5 mm and with the BIA over 0.80. Our invention is remarkably characterized by an adequate sectional area A even when B/A is large, thus providing the great advantage of being able to increase the power. A circular type has no such advantage.

It is noted that the slits illustrated in the drawings have been simplified to facilitate understanding of the present invention and do not represent the correct width and length dimensions, as specifically recited in the examples.

We claim:

1. A plasma jet nozzle for directing a flame in the form of a thin film comprising an elongated narrow passage having a pair of smooth generally longitudinally straight opposed side walls equidistantly spaced from each other over their entire surfaces and a pair of smooth generally longitudinally straight opposed end walls, said side and end walls defining a slotted transverse inlet opening atone end of the passage and a slotted transverse outlet opening at the other end of the passage, one end of the nozzle being provided with a transversely disposed concave inlet surface generally complementary to the end surface of an electrode rod to be positioned in axially spaced relationship to said inlet surface, said pairs of side and end walls all intersecting said concave inlet surface at one end of the passage and terminating at said intersection to provide an unobstructed space completely surrounding the tip of an electrode rod and lying between said tip and the concave surface for gases entering the inlet opening of said passage, the outer diameter of said concave surface being at least equal to the transverse length of the passage at the intersection of the passage and concave surface, whereby gases move through the passage from inlet opening to outlet opening in longitudinally straight directions.

2. A plasma jet nozzle as defined in claim 1, wherein the end walls of the passage diverge in the direction toward the outlet opening of the passage.

3. A plasma jet nozzle as defined in claim 1, wherein the side walls of the passage are arcuate in transverse cross-section to define a narrow curved outlet opening.

4. A plasma jet nozzle as defined in claim 1, wherein the exterior of said nozzle includes at least one heatconducting cooling fin.

5. A plasma jet nozzle as defined in claim 1, wherein the ratio of the length of the wall surrounding said passage to the cross-sectional area of the pasasage is greater than 1.00.

6. A plasma jet nozzle as defined in claim 1, wherein the ratio of the length of the wall surrounding said passage to the cross-sectional area of the passage is greater than 1.20.

7. A plasma jet nozzle as defined in claim 1, wherein the transverse width of said passage is less than 2.5 mm.

8. A plasma jet torch comprising an elongated housing having a nozzle at one end and inlet means at the other end for gases and cooling fluid, the interior of the housing being provided with a first cylindrical conduit in communication with the nozzle at one end and with the inlet means at the other end for conducting gases to said nozzle, a second cylindrical conduit surrounding said first conduit in concentric relationship thereto and in communication with said inlet means, said second conduit forming with said first conduit a passage for circulating cooling fluid in heat-exchanging relationship with said first conduit, said nozzle being provided with an interior longitudinally extending passage having a narrow slotted inlet opening at one end and a narrow slotted outlet opening at the other end generally similar to and in axial alignment with said inlet opening, an elongated electrode rod concentrically positioned in said first conduit having an exposed tip spaced from and in axial alignment with the slotted inlet opening of the nozzle, the interior walls of said first conduit and said passage in the nozzle being smooth and defined by longitudinally extending straight lines whereby gases moving from said inlet means of the torch to the outlet opening of the nozzle do not acquire any spiral motion.

9. A plasma jet torch as defined in claim 8, wherein the outlet opening of the nozzle has a deflected configuration.

10. A plasma jet torch as defined in claim 8, wherein said nozzle is provided with at least two slotted outlet openings in communication with the internal passage.

1 l. A plasma jet torch as defined in claim 8, wherein at least a portion of the outlet opening of the nozzle has an L-shaped configuration in transverse cross-section.

12. A plasma jet torch as defined in claim 8, wherein the outlet opening of the nozzle has an arcuate configuration in transverse cross-section.

13. A plasma jet torch as defined in claim 8, wherein the outlet opening of the nozzle has an X-shaped configuration in transverse cross-section.

14. A plasma jet torch as defined in claim 8, wherein said nozzle is also provided with at least one discharge orifice for a fluid under pressure adjacent said outlet opening. 

1. A plasma jet nozzle for directing a flame in the form of a thin film comprising an elongated narrow passage having a pair of smooth generally longitudinally straight opposed side walls equidistantly spaced from each other over their entire surfaces and a pair of smooth generally longitudinally straight opposed end walls, said side and end walls defining a slotted transverse inlet opening at one end of the passage and a slotted transverse outlet opening at the other end of the passage, one end of the nozzle being provided with a transversely disposed concave inlet surface generally complementary to the end surface of an electrode rod to be positioned in axially spaced relationship to said inlet surface, said pairs of side and end walls all intersecting said concave inlet surface at one end of the passage and terminating at said intersection to provide an unobstructed space completely surrounding the tip of an electrode rod and lying between said tip and the concave surface for gases entering the inlet opening of said passage, the outer diameter of said concave surface being at least equal to the transverse length of the passage at the intersection of the passage and concave surface, whereby gases move through the passage from inlet opening to outlet opening in longitudinally straight directions.
 2. A plasma jet nozzle as defined in claim 1, wherein the end walls of the passage diverge in the direction toward the outlet opening of the passage.
 3. A plasma jet nozzle as defined in claim 1, wherein the side walls of the passage are arcuate in transverse cross-section to define a narrow curved outlet opening.
 4. A plasma jet nozzle as defined in claim 1, wherein the exterior of said nozzle includes at least one heat-conducting cooling fin.
 5. A plasma jet nozzle as defined in claim 1, wherein the ratio of the length of the wall surrounding said passage to the cross-sectional area of the pasasage is greater than 1.00.
 6. A plasma jet nozzle as defined in claim 1, wherein the ratio of the length of the wall surrounding said passage to the cross-sectional area of the passage is greater than 1.20.
 7. A plasma jet nozzle as defined in claim 1, wherein the transverse width of said passage is less than 2.5 mm.
 8. A plasma jet torch comprising an elongated housing having a nozzle at one end and inlet means at the other end for gases and cooling fluid, the interior of the housing being provided with a first cylindrical conduit in communication with the nozzle at one end and with the inlet means at the other end for conducting gases to said nozzle, a second cylindrical conduit surrounding said first conduit in concentric relationship thereto and in communication with said inlet means, said second conduit forming with said first conduit a passage for circulating cooling fluid in heat-exchanging relationship with said first conduit, said nozzle being provided with an interior longitudinally extending passage having a narrow slotted inlet opening at one end and a narrow slotteD outlet opening at the other end generally similar to and in axial alignment with said inlet opening, an elongated electrode rod concentrically positioned in said first conduit having an exposed tip spaced from and in axial alignment with the slotted inlet opening of the nozzle, the interior walls of said first conduit and said passage in the nozzle being smooth and defined by longitudinally extending straight lines whereby gases moving from said inlet means of the torch to the outlet opening of the nozzle do not acquire any spiral motion.
 9. A plasma jet torch as defined in claim 8, wherein the outlet opening of the nozzle has a deflected configuration.
 10. A plasma jet torch as defined in claim 8, wherein said nozzle is provided with at least two slotted outlet openings in communication with the internal passage.
 11. A plasma jet torch as defined in claim 8, wherein at least a portion of the outlet opening of the nozzle has an L-shaped configuration in transverse cross-section.
 12. A plasma jet torch as defined in claim 8, wherein the outlet opening of the nozzle has an arcuate configuration in transverse cross-section.
 13. A plasma jet torch as defined in claim 8, wherein the outlet opening of the nozzle has an X-shaped configuration in transverse cross-section.
 14. A plasma jet torch as defined in claim 8, wherein said nozzle is also provided with at least one discharge orifice for a fluid under pressure adjacent said outlet opening. 